1. Field of the Invention
The present disclosure relates to a switching power supply apparatus that controls an output voltage by switching of an input voltage through a switching element, and a device connection state detection circuit.
2. Description of the Related Art
In recent years, environmental problems such as an energy problem have been noticed, and there is a strong demand on reduction in standby power of a power supply apparatus such as a switching power supply apparatus. For example, there is proposed a system for lowering an output voltage to reduce power consumption, in a case where power supply from a switching power supply apparatus is unnecessary, for example in a state where a load device is not connected, in an AC adapter or a battery charger.
There is proposed a conventional, technology of detecting presence/absence of a load of an AC adapter, stopping operation of a switching power supply apparatus to reduce power consumption when an output side is in an unloaded condition, and further restarting operation to start power supply when a voltage is applied from a load device connected to the output side, in Unexamined Japanese Patent Publication No. 2007-14339 (PTL 1).
As a power supply of the load device, a power storage component such as a primary battery and a secondary battery is conceivably used.
FIG. 22 illustrates a configuration example of a conventional switching power supply apparatus, in which operation of the switching power supply apparatus is stopped when the output side is in an unloaded condition, and the operation is restarted when a voltage is applied to the output side from the load device. Hereinafter, the operation of the switching power supply apparatus is briefly described.
A loaded condition of secondary load device 912 is monitored by output control circuit 911 through resistor 909. In a case where an unloaded condition is detected, a no-load detection signal is input to power ON/OFF circuit 905 from output control circuit 911 through coupler circuit 906. Then, when an operation stop signal is input to drive control circuit 901 of switching control circuit 900 from power ON/OFF circuit 905, drive control circuit 901 controls drive circuit 902 so as to stop operation of switching element 7. Then, an output voltage of the switching power supply apparatus becomes zero.
In a case where the operation of the switching power supply apparatus is restarted, when the output voltage is zero, a voltage is applied from a power storage unit (not illustrated) of load device 912 through output terminal 16, so that output control circuit 911 detects that the output voltage is not zero. Then, by use of this voltage as a power supply, output control circuit 911 inputs a restart signal to power ON/OFF circuit 905 through photocoupler 910. At the same time, generation of an operation stop signal from power ON/OFF circuit 905 is stopped for a fixed period. When an operation start signal is input to drive control circuit 901 from power ON/OFF circuit 905, drive control circuit 901 controls drive circuit 902 so as to start the operation of switching element 7.
By use of this technology, it is possible to implement a system, in which when the switching power supply apparatus (e.g., AC adapter) is not connected to the load device (e.g., notebook computer) (unloaded condition), the switching operation of the switching power supply apparatus can be stopped to reduce power consumption (off mode), and when the switching power supply apparatus is connected to the load device, and a voltage is applied from the power storage component (e.g., battery) of the load device, the switching power supply apparatus starts power supply, for example.